.header{
    margin:0 auto;
    width: 100%;
    height:100px;
    background-color: blue;
}

.content{
    margin: 0 auto;
    max-width: 1200px;
    height: 800px;
    background-color: aquamarine;
}
.footer{
    margin: 0 auto;
    width: 100%;
    height: 100px;
    background-color: aqua;
}